The Water Era, Understanding Water. Shaping the Future.

Wastewater Reuse: Turning Used Water into a Resource

Discover how wastewater reuse can support agriculture and industry, while advanced treatment enables safe drinking-water applications under strict controls.

PCT

11/15/20267 min leer

From Wastewater to Drinking Water: A New Frontier in Technology

How advanced membranes, reverse osmosis and disinfection systems are making it possible to recover used water and turn it into a resource for the future.

1. The Water We Use Does Not Have to Disappear

Every day, millions of people use water for drinking, cooking, showering, washing, irrigation and industrial activities.

After use, a significant proportion of this water becomes wastewater and reaches treatment plants through sewerage systems.

For many years, the main objective has been to remove contaminants and return the water to the natural environment in suitable conditions.

However, today, with water scarcity affecting many regions of the world, science and technology are encouraging a different way of looking at this process.

What if, instead of considering used water as waste, we treated it as a resource that could have a new life?

This is the principle behind water reuse: recovering water after use, subjecting it to the necessary treatment processes and putting it back into the cycle of human activity.

It is not simply a matter of treating wastewater. It is about achieving a quality suitable for each new purpose, from agricultural irrigation and industrial processes to certain drinking-water applications, when the treatment processes and health safeguards allow it.

2. How Is Wastewater Transformed into Reusable Water?

The process begins at wastewater treatment plants, where water passes through several treatment stages.

Not all facilities use exactly the same systems. The technology required depends on the initial water quality and its intended final use.

Generally, the process involves several stages.

First stage: removing waste and particles.

When water reaches the facility, it passes through screens, sieves and separation systems that remove plastics, sand, grease and other solid materials.

Afterwards, in certain treatment processes, suspended solids are separated through sedimentation.

Second stage: biological treatment.

At this stage, microorganisms break down a significant proportion of the organic matter present in the water.

This is an essential process because it reduces the pollutant load before the water moves on to further treatment stages.

Third stage: advanced treatment.

When higher-quality water is required, more sophisticated technologies can be introduced, including microfiltration, ultrafiltration, reverse osmosis, activated carbon and ultraviolet disinfection.

These technologies make it possible to reduce contaminants that conventional treatment processes do not necessarily remove with the same effectiveness.

3. Membranes: One of the Major Advances in Water Treatment

One of the most important technologies in advanced water reuse is membrane filtration.

We can think of a membrane as an extremely fine barrier that separates water from some of the materials it contains, whether suspended or dissolved.

There are different types of membranes.

Microfiltration and ultrafiltration

These technologies use membranes with very small pores to retain particles, microorganisms and other elements, depending on the pore size and the characteristics of the system.

Reverse osmosis

This is an even more demanding technology.

Using pressure, water passes through a semipermeable membrane that allows water molecules to pass while retaining a large proportion of dissolved salts and other contaminants.

It is particularly important when very high-purity water is required.

Ultraviolet disinfection

After other treatment stages, ultraviolet radiation can inactivate microorganisms such as bacteria and viruses.

Some systems also incorporate other processes, such as activated carbon or advanced oxidation, to control specific contaminants.

Combining these technologies makes it possible to obtain reclaimed water with characteristics very different from those of the original wastewater.

4. Is All Reused Water Suitable for Drinking?

No. This distinction is essential to understanding the technology correctly.

Water reuse can have different destinations.

Non-potable reuse

This is one of the most widespread applications. Reclaimed water can be used for crop irrigation, green spaces, street cleaning, certain industrial processes and other purposes that do not require drinking-water quality.

This type of reuse can reduce the need to extract freshwater from rivers, reservoirs and aquifers.

Indirect potable reuse

In this case, reclaimed water receives advanced treatment and is then introduced into a reservoir, river or aquifer.

It subsequently undergoes further treatment at a drinking-water treatment plant before being distributed for human consumption.

The natural environment or a storage system acts as an intermediate stage.

Direct potable reuse

This is a more demanding system. After receiving advanced treatment and undergoing specific controls, reclaimed water is introduced into the drinking-water supply system without passing through a natural reservoir, river or aquifer as an intermediate stage.

This approach requires multiple treatment barriers, continuous monitoring, safety protocols and very rigorous health controls.

Not all regions have the same regulations or the same conditions for developing these systems.

Singapore: An Example of Water Reuse on a Large Scale

One of the best-known examples of advanced water reuse is the NEWater programme, developed by Singapore's public water agency, PUB.

Singapore has invested in recovering treated wastewater and subjecting it to advanced purification processes to produce high-quality reclaimed water.

The NEWater system uses three main stages:

  1. Microfiltration or ultrafiltration: removes particles and bacteria.

  2. Reverse osmosis: separates a large proportion of dissolved salts and other contaminants.

  3. Ultraviolet disinfection: inactivates any remaining microorganisms.

Singapore currently has four NEWater plants in operation, according to the public agency responsible for water management.

Most of this water is used for industrial purposes and cooling systems. During dry periods, a proportion is added to reservoirs, where it mixes with existing water before undergoing further conventional treatment for human consumption.

This is an example of indirect potable reuse, rather than the direct introduction of reclaimed water into household taps.

The importance of NEWater lies in demonstrating how advanced water reuse can become a structural part of a region's water security.

Source: PUB Singapore – NEWater.

6. Europe Is Also Moving Towards Water Reuse

Water reuse is becoming increasingly important in Europe, especially in regions affected by water scarcity and prolonged drought.

The European Commission indicates that approximately one billion cubic metres of treated urban wastewater are reused annually in the European Union, and that the potential for water reuse could be six times higher than the current level.

European legislation on water reuse, Regulation (EU) 2020/741, applicable since 26 June 2023, establishes minimum quality, monitoring and risk-management requirements for the reuse of treated urban wastewater intended for agricultural irrigation.

It is important to clarify that this regulation concerns agricultural irrigation. It does not, by itself, constitute general authorisation to use reclaimed water as drinking water.

There are also developments in potable reuse.

A study published in 2026 in the journal Water Reuse examines a direct potable reuse facility in Aalst, Flanders (Belgium), which was commissioned in 2025.

The facility has a production capacity of 50 cubic metres per hour and uses several treatment barriers: ultrafiltration, reverse osmosis, ultraviolet radiation, activated carbon filtration and final disinfection using ultraviolet radiation and chlorine.

It is an example of how these technologies are also beginning to find real-world applications in Europe.

Sources:

7. Is Reclaimed Water Really Safe?

This is one of the most important questions and also one of the issues that concerns the public most.

Safety does not depend on a single membrane or one disinfection process.

It depends on combining different treatment barriers, the initial quality of the water, contaminant control, monitoring and supervision of the entire process.

Both microbiological and chemical risks must be controlled.

It is also necessary to verify that the systems are operating correctly and that the water meets the standards required for its intended use.

The World Health Organization, in its updated 2026 edition of the Guidelines for Drinking-water Quality, emphasises the importance of managing risks from the source of the water all the way to the consumer, through health-based targets, water safety plans and independent surveillance.

This approach is essential to ensuring water quality, particularly when the water comes from reused sources.

Source: WHO – Guidelines for Drinking-water Quality, 2026.

8. The Challenges We Still Need to Overcome

Advanced water reuse offers important possibilities, but it is not without its disadvantages.

Energy consumption

Processes such as reverse osmosis require energy to operate pumps and maintain the necessary pressure.

It is therefore important to improve the efficiency of treatment plants and explore the possibility of powering them with renewable energy.

Concentrates and waste

Membranes separate contaminants, but these do not disappear. They remain concentrated in another fraction of water that must be managed appropriately.

Cost of facilities

Advanced treatment plants require investment, maintenance, specialised personnel and permanent monitoring systems.

Public confidence

People need to understand how the process works, what controls are carried out and what health safeguards are in place.

Transparency and scientific information are just as important as the technology itself.

9. Towards a New Water Economy

For many years, water management has been based mainly on collecting water, using it, treating it and returning it to the environment.

Advanced water reuse introduces a different perspective: extending the cycle of water use and reducing dependence on available natural sources.

This does not mean that all wastewater should be converted into drinking water.

In many cases, it is more efficient to use reclaimed water for agricultural, industrial or cleaning purposes, reserving the highest-quality drinking water for uses that genuinely require it.

The key is to match water quality to its intended purpose and manage each resource according to technical, economic and environmental criteria.

This approach is part of the circular economy: making better use of resources, reducing waste and avoiding unnecessary consumption of new water supplies.

Conclusion: The Future of Water Also Depends on Recovering What We Have Already Used

Advanced water reuse shows us that part of the solution to water scarcity may lie in resources we already have.

Membranes, reverse osmosis, ultraviolet disinfection and advanced monitoring systems are transforming the way we can recover and reuse water.

They do not replace the need to protect rivers, aquifers, reservoirs and natural ecosystems. Nor do they eliminate the need to reduce consumption and improve the efficiency of distribution networks.

However, they can provide an additional source of supply and strengthen water security in many regions.

Perhaps the major change in mindset we need is to stop considering used water as the end of a process.

Water does not necessarily lose its value after its first use. With the right technology, it can become part of our future once again.

The Water Era — Understanding Water. Shaping the Future.

At EnergeticWater, we explore how science, water and innovation can help address humanity's major water challenges.

Image: Modern facility for advanced water treatment and reclamation using sustainable technologies.

Pere Castells Teulats

Scientific researcher and science communicator

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